EP0098665A2 - Démodulateur de données pour un signal à modulation de fréquence directe - Google Patents

Démodulateur de données pour un signal à modulation de fréquence directe Download PDF

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Publication number
EP0098665A2
EP0098665A2 EP83200994A EP83200994A EP0098665A2 EP 0098665 A2 EP0098665 A2 EP 0098665A2 EP 83200994 A EP83200994 A EP 83200994A EP 83200994 A EP83200994 A EP 83200994A EP 0098665 A2 EP0098665 A2 EP 0098665A2
Authority
EP
European Patent Office
Prior art keywords
outputs
frequency
data demodulator
summing
providing
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP83200994A
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German (de)
English (en)
Other versions
EP0098665A3 (fr
Inventor
Christopher Brian Marshall
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Philips Electronics UK Ltd
Koninklijke Philips NV
Original Assignee
Philips Electronic and Associated Industries Ltd
Philips Electronics UK Ltd
Philips Gloeilampenfabrieken NV
Koninklijke Philips Electronics NV
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Philips Electronic and Associated Industries Ltd, Philips Electronics UK Ltd, Philips Gloeilampenfabrieken NV, Koninklijke Philips Electronics NV filed Critical Philips Electronic and Associated Industries Ltd
Publication of EP0098665A2 publication Critical patent/EP0098665A2/fr
Publication of EP0098665A3 publication Critical patent/EP0098665A3/fr
Withdrawn legal-status Critical Current

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Classifications

    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L27/00—Modulated-carrier systems
    • H04L27/10—Frequency-modulated carrier systems, i.e. using frequency-shift keying
    • H04L27/14—Demodulator circuits; Receiver circuits
    • H04L27/144—Demodulator circuits; Receiver circuits with demodulation using spectral properties of the received signal, e.g. by using frequency selective- or frequency sensitive elements
    • H04L27/152—Demodulator circuits; Receiver circuits with demodulation using spectral properties of the received signal, e.g. by using frequency selective- or frequency sensitive elements using controlled oscillators, e.g. PLL arrangements
    • H04L27/1525—Demodulator circuits; Receiver circuits with demodulation using spectral properties of the received signal, e.g. by using frequency selective- or frequency sensitive elements using controlled oscillators, e.g. PLL arrangements using quadrature demodulation

Definitions

  • the present invention relates to a data demodulator for a direct frequency modulated signal, for example a frequency shift keying (FSK) signal used in a quasi-synchronous signalling system such as paging,
  • FSK frequency shift keying
  • Direct frequency modulation is a convenient and commonly used form of modulation.
  • a direct frequency modulated signal is easily demodulated by a phase lock loop or a pair of bandpass filters having central frequencies located at the deviation frequency on either side of the carrier frequency.
  • a disadvantage of superheterodyne receivers is that they produce a spurious image response which can be removed by R.F. filtering.
  • R.F. filtering means that the receiver circuit is unsuitable for fabrication by integration which is desirable for a low cost and low power consuming receiver such as a pager.
  • Direct conversion or zero I.F. receivers are more suitable for fabrication by integration but cannot use conventional demodulators.
  • British Patent Specification 1,127,451 discloses a frequency- shift detection circuit for carrier shift telegraphy.
  • the circuit comprises first and second switching modulators both of which receive an input signal and a local oscillator signal which in the case of the second switching modulator lags by 90 the local oscillator signal applied to the first switching modulator.
  • the output from the first switching modulator is advanced in phase by 90 0 and applied to an input of a signal combining network.
  • the output of the second switching modulator which output lags the phase advanced output of the first switching modulator by 180°, is applied to another input of the signal combining network.
  • the applied signals undergo additive or subtractive combinationo Low pass filters are connected to the respective outputs to pass the deviation frequency and reject the higher frequencies present in the combined signals.
  • decoding of demodulated telegraphic signals may be done by using one or other or both the outputs from the combining circuit.
  • Such a simple circuit operates satisfactorily at low bit rates up to a maximum bit rate of half the deviation frequency but is not suitable for use with higher bit rate signals.
  • British Patent Specification 2,101,821A discloses a radio receiver for frequency shift keyed (FSK) signals of the zero IF type.
  • the quadrature outputs of a pair of mixers are low-pass filtered and a 90 o phase shift at the baseband frequency is introduced in one signal path.
  • These baseband signals are then fully limited and are applied to a logic network, for example an exclusive-OR gate, to provide a digital output indicative of the lead/lag condition of the two signal paths.
  • This particular receiver is only able to handle a low rate of signalling because of limitations on the switching speed of the exclusive-OR gate also there are constraints in the operation of the limiting amplifiers.
  • Figures 3 and 5 of this specification suggest duplicating the signal paths and having a 45 0 phase difference between the signals in one pair of paths and the signals in the duplicate pair of paths.
  • a data demodulator for a direct frequency modulated signal comprising means providing a positive frequency filter and a negative frequency filter, said filters each having a pass band that includes the modulus of the deviation frequency and providing outputs with two different phases for the positive frequency and two different phases for the negative frequency and means for comparing the signal strength in the outputs of the positive and negative frequency filters to provide a data output.
  • the means providing the positive and negative frequency filters comprise first and second quadrature mixers, first filter means coupled to the output of the first mixer for providing first and second outputs having a relative phase shift of 90 0 therebetween, second filter means coupled to the output of the second mixer for providing third and fourth outputs having a relative phase shift of 90 0 therebetween, the first and fourth outputs and the second and third outputs comprising in-phase or anti-phase pairs of outputs, first summing means for summing the first and fourth outputs, first differencing means for producing the difference of the second and third outputs, the first summing means and the first differencing means providing outputs for the positive input frequencies, second summing means for summing the second and third outputs, and second differencing means for producing the difference of the first and fourth outputs, the second summing means and the second differencing means providing outputs for the negative input frequencies.
  • the means for comparing the signal strength in the outputs of the positive and negative frequency filters may include amplitude detectors for detecting the amplitudes of output signals from the first and second summing means and the first and second differencing means and a difference amplifier.
  • amplitude detectors may comprise full wave rectifiers.
  • the data demodulator shown in Figure 1 comprises an input terminal 10 which is connected to respective first inputs of mixers 12, 14.
  • a local oscillator 16 having the same frequency, f , as the carrier frequency is connected to the second input of the mixer 14 and, via a quadrature phase shifter 18, to a second input of the mixer 12.
  • the combined effect of the quadrature mixers 12, 14 and the phase shifter 18 is to produce a pair of signals such that in the case of ⁇ f > 0 the waveform A leads the waveform B by 90 0 but in the case of ⁇ f ⁇ 0 the waveform A lags the waveform B by 90°.
  • the waveforms A and B are applied to quadrature phase shifting stages 24, 26 which produce the outputs illustrated by the waveforms C and D. If necessary the phase of the waveforms A and B can be adjusted using phase shifting stages 28, 30, the outputs of which are shown by waveforms A' and B', to achieve quadrature between the outputs 24 and 28 and between 26 and 30 over a wider range of frequencies.
  • the 90 o phase shifted signals that is the waveforms C and D, are applied to the negative (or inverting) inputs.
  • the waveforms E, F, G and H are then amplitude or envelope detected by, for example, full wave rectifiers 40, 42, 44, 46 coupled respectively to the outputs of the circuits 32, 36, 38, 34.
  • the outputs of the full wave rectifiers 40, 42, 44 and 46 are illustrated by the waveforms K, L, M and N, respectively.
  • signals, waveforms R and S are obtained which do not go to zero, unlike the respective outputs of the full wave rectifiers 40, 42, 44 and 46.
  • the D.C. levels in the outputs of the summing circuits 48, 50 are indicative of the sign of the frequency displacement, that is +/A f or - ⁇ f from the carrier frequency f c and hence the modulation.
  • the outputs of the summing circuits 48, 50 are subtracted from each other in a subtracting circuit 52.
  • smoothing by low pass filtering may be provided by filters 54, 56 connected to the inputs of the subtracting circuit 52 or a filter 58 connected to the output of the circuit 52.
  • the data rate can be increased by up to twice the deviation frequency compared to around half of the deviation frequency ⁇ f when not duplicating the signal processing. Additionally the signal-to-noise ratio is improved due to an increased openness of the "eye" diagram.
  • any means of forming positive + ⁇ f and negative -6f frequency filters with quadrature phase outputs can be used, for example polyphase filters, the different phase outputs being applied to the respective full wave rectifiers 40, 42, 44 and 46.
  • the data demodulator operates at baseband then there is no requirement for R.F. filters which means that the demodulator can be fabricated by integrated circuit techniques.
  • the low pass filters 20 and 22 can be used to do channel selectivity, that is to remove the adjacent channel.

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  • Physics & Mathematics (AREA)
  • Spectroscopy & Molecular Physics (AREA)
  • Engineering & Computer Science (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Signal Processing (AREA)
  • Digital Transmission Methods That Use Modulated Carrier Waves (AREA)
EP83200994A 1982-07-07 1983-07-05 Démodulateur de données pour un signal à modulation de fréquence directe Withdrawn EP0098665A3 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
GB8219631 1982-07-07
GB08219631A GB2124046A (en) 1982-07-07 1982-07-07 Data demodulator for a direct frequency modulated signal

Publications (2)

Publication Number Publication Date
EP0098665A2 true EP0098665A2 (fr) 1984-01-18
EP0098665A3 EP0098665A3 (fr) 1984-05-30

Family

ID=10531518

Family Applications (1)

Application Number Title Priority Date Filing Date
EP83200994A Withdrawn EP0098665A3 (fr) 1982-07-07 1983-07-05 Démodulateur de données pour un signal à modulation de fréquence directe

Country Status (5)

Country Link
EP (1) EP0098665A3 (fr)
JP (1) JPS5923662A (fr)
AU (1) AU1655983A (fr)
DK (1) DK308183A (fr)
GB (1) GB2124046A (fr)

Families Citing this family (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CH667170A5 (de) * 1984-12-07 1988-09-15 Industrieorientierte Forsch Verfahren zur detektion der information eines empfangssignales, insbesondere mit frequenzumtastung.
US5400365A (en) * 1992-05-21 1995-03-21 Mitel Corporation Isk receiver

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB1127451A (en) * 1965-02-04 1968-09-18 Ass Elect Ind Improvements relating to carrier shift telegraphy
FR2391593A1 (fr) * 1977-05-20 1978-12-15 Philips Nv Etage de transposition en quadrature
US4156194A (en) * 1977-09-06 1979-05-22 General Electric Company Frequency-shift-keyed receiver
GB2057820A (en) * 1979-09-04 1981-04-01 Standard Telephones Cables Ltd Radio receiver for fsk signals

Family Cites Families (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2101821B (en) * 1981-07-16 1984-11-14 Standard Telephones Cables Ltd Radio receiver for frequency shift keyed signals

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB1127451A (en) * 1965-02-04 1968-09-18 Ass Elect Ind Improvements relating to carrier shift telegraphy
FR2391593A1 (fr) * 1977-05-20 1978-12-15 Philips Nv Etage de transposition en quadrature
US4156194A (en) * 1977-09-06 1979-05-22 General Electric Company Frequency-shift-keyed receiver
GB2057820A (en) * 1979-09-04 1981-04-01 Standard Telephones Cables Ltd Radio receiver for fsk signals

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
ELECTRICAL COMMUNICATION, vol. 48, no. 1,2, 1973, pages 21-25, London, GB M.J. GINGELL: "Single sideband modulation using sequence asymmetric polyphase networks" *

Also Published As

Publication number Publication date
EP0098665A3 (fr) 1984-05-30
AU1655983A (en) 1984-01-12
GB2124046A (en) 1984-02-08
JPS5923662A (ja) 1984-02-07
DK308183D0 (da) 1983-07-04
DK308183A (da) 1984-01-08

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